The Middle East respiratory syndrome coronavirus (MERS-CoV) utilizes host proteases for virus entry into lung cells. In the current study, Vero cells constitutively expressing type II transmembrane serine protease (Vero-TMPRSS2 cells) showed larger syncytia at 18 h after infection with MERS-CoV than with other coronaviruses. Furthermore, the susceptibility of Vero-TMPRSS2 cells to MERS-CoV was 100-fold higher than that of non-TMPRSS2-expressing parental Vero cells. The serine protease inhibitor camostat, which inhibits TMPRSS2 activity, completely blocked syncytium formation, but only partially blocked virus entry into Vero-TMPRSS2 cells. Importantly, the coronavirus is thought to enter cells via two distinct pathways, one mediated by TMPRSS2 at the cell surface, and the other mediated by cathepsin L in the endosome. Simultaneous treatment with inhibitors of cathepsin L and TMPRSS2 completely blocked virus entry into Vero-TMPRSS2 cells, indicating that MERS-CoV employs both the cell surface and the endosomal pathway to infect Vero-TMPRSS2 cells. By contrast, a single camostat treatment suppressed MERS-CoV entry into human bronchial submucosal gland-derived Calu-3 cells by 10-fold and virus growth by 270-fold, although treatment with both camostat and EST, a cathepsin inhibitor, or treatment with leupeptin, an inhibitor of cysteine, serine, and threonine peptidases, was no more efficacious than camostat alone. Further, these inhibitors were not efficacious against MERS-CoV infection of MRC-5 and WI-38 cells which derived from lung but these characters differ from mature pneumocytes. These results suggest that a single treatment with camostat is sufficient to block MERS-CoV entry into a well-differentiated lung-derived cell line.